Rotary Equipment in Operative Dentistry

Definition

Classification of Speeds

Development of Rotary Equipment

1. Hand-operated instruments

• In the earliest period, caries was removed using hand excavators, chisels and spoon excavators.
• This method was slow, tiring and produced considerable discomfort to the patient.

2. Hand drill or bow drill

• Early dental drills were operated manually by rotating a handle or bow.
• They had very low speed and poor cutting efficiency.

3. Foot-powered drill

• Foot treadle dental engines were introduced in the nineteenth century.
• The operator used a foot pedal to drive a belt system.
• The speed was higher than that of hand drills but still low, and the equipment was bulky.

4. Belt-driven dental engine

• The belt-driven dental engine was developed further with pulley systems and flexible arms.
• It permitted continuous rotation of burs and improved cavity preparation.
• Conventional gear-driven handpieces of the 1950s operated around 6,500 rpm and could overheat at higher speeds because of metal-to-metal friction, as described by the University of the Pacific Dental Museum.

5. Electric motor-driven handpiece

• Electric motors replaced foot-driven power in many units.
• Contra-angle handpieces and reduction gears improved access to posterior teeth.
• These handpieces were useful at low and medium speeds, especially for finishing and polishing.

6. Air-turbine handpiece

• The major advance in rotary instrumentation was the introduction of the air-turbine handpiece in the 1950s.
• John Borden's Airotor made high-speed dentistry clinically practical.
• Compressed air rotates a small turbine carrying a friction-grip bur.
• It made cutting faster, smoother and more comfortable, with less vibration and pressure.

7. Modern electric and air-rotor systems

• Present-day dental units provide air-driven and electric high-speed handpieces, fibre-optic illumination, water-air spray, anti-retraction valves and improved bearings.
• Electric high-speed handpieces provide greater torque and more constant speed under load, while air turbines provide very high rotational speeds.

Merits and Demerits of Various Speeds

A. Low-speed rotary instruments

Merits

1. Good tactile sensation
   • The operator can feel differences between soft carious dentin and sound dentin.
   • Useful for controlled caries removal.
2. Good torque
   • Low-speed handpieces have relatively greater torque.
   • They do not stall as easily during polishing, finishing and excavation.
3. Safer near soft tissues
   • Less chance of accidental severe injury to lips, cheeks, tongue or gingiva.
4. Useful for finishing procedures
   • Used for finishing restorations, polishing, prophylaxis, stain removal and use of rubber cups.
5. Less aerosol production
   • Produces less aerosol and splatter than air-turbine instrumentation.
6. Economical and simple
   • Low-speed attachments are generally less expensive and easier to maintain.

Demerits

1. Slow cutting
   • Inefficient for cutting enamel, dentin and old metallic restorations.
2. More pressure required
   • Greater operator pressure is needed, causing fatigue and patient discomfort.
3. More vibration
   • At slow speed with high pressure, vibration may be transmitted to the tooth and patient.
4. Heat production
   • If pressure is excessive or the bur is dull, heat may be produced.
5. Not suitable for routine cavity preparation
   • Not ideal for rapid removal of tooth structure.

B. Medium-speed rotary instruments

Merits

1. Faster cutting than low speed.
2. Better efficiency for some finishing and cutting procedures.
3. Useful in older rotary systems and selected laboratory work.
4. Less expensive than some high-speed units.

Demerits

1. Cutting efficiency is still lower than high or ultra-high speeds.
2. Greater vibration may occur.
3. Heat generation may be significant if water coolant is inadequate.
4. Limited use in modern operative dentistry because high-speed systems are superior for cavity preparation.

C. High-speed rotary instruments

Merits

1. Rapid cutting
   • Enables quick preparation of enamel and dentin.
   • Reduces chairside time.
2. Less pressure required
   • Cutting is achieved with light intermittent strokes.
   • This reduces patient discomfort and operator fatigue.
3. Less vibration
   • Smooth cutting occurs when a sharp bur is used with adequate water spray.
4. Efficient cavity preparation
   • Useful for cutting enamel, preparing cavities, removing old restorations, crown preparation and sectioning teeth where indicated.
5. Better patient acceptance
   • Shorter operating time and reduced pressure usually improve patient comfort.
6. Conservative cavity preparation
   • Small friction-grip burs permit more precise and conservative preparations.

Demerits

1. Heat production
   • High-speed cutting can produce dangerous heat.
   • A continuous air-water spray is mandatory to prevent pulpal injury.
2. Reduced tactile sensation
   • The operator may inadvertently remove excessive tooth structure.
3. Risk of soft-tissue injury
   • Lips, cheeks, tongue, gingiva and fingers can be injured if the bur slips.
4. Aerosol and splatter
   • Air turbines generate aerosol containing saliva, blood and microorganisms.
   • This requires high-volume evacuation, personal protective equipment and infection-control measures. A review of rotary handpieces classified high-speed devices broadly in the 200,000-400,000 rpm range and discussed aerosol generation with their use in this PMC review.
5. Poor torque in air turbines
   • Air-turbine handpieces may slow down or stall when excessive pressure is applied.
6. Noise and patient anxiety
   • The high-pitched sound can create fear, particularly in children and anxious patients.
7. Risk of pulpal damage
   • Excessive pressure, dull burs, prolonged cutting at one spot, or inadequate coolant can cause thermal injury to the pulp.

D. Ultra-high-speed air-turbine instruments

Merits

1. Highest cutting efficiency for enamel and dentin.
2. Very little pressure is required.
3. Reduces duration of cavity and crown preparation.
4. Produces a smoother cavity preparation with proper technique.
5. Useful for conservative operative procedures using small friction-grip burs.
6. Improves access in posterior regions because the handpiece head is small.

Demerits

1. Very low torque compared with electric high-speed systems.
2. Bur may stop when heavy pressure is applied.
3. Requires effective water cooling and high-volume suction.
4. Produces aerosol, noise and splatter.
5. Increased risk of accidental soft-tissue trauma.
6. Maintenance is costly because turbine bearings may wear out.
7. Cannot be used safely for all surgical bone-cutting procedures unless a suitable surgical handpiece and sterile coolant system are used.

Conclusion